Current alkali-metal magnetometers can surpass SQUIDs as the most sensitive detectors of a magnetic field, reaching a sensitivity below 1 fT/Hz1/2 (I. K. Kominis, et al., Nature (London) 422, 596 (2003); H. B. Dang, et al., Appl. Phys. Lett. 97, 151110 (2010)), but only if they are operated near zero-magnetic field to eliminate spin relaxation due to spin-exchange collisions (W. Happer, et al., Phys. Rev. Lett. 31, 273 (1973); J. C. Allred, et al., Phys. Rev. Lett. 89, 130801 (2002)). Many magnetometer applications, such as searches for permanent electric dipole moments (A. Weis, et al., Nucl. Instrum. Methods Phys. Res., Sect. A 611, 306 (2009)), detection of NMR signals (M. P. Ledbetter, et al., Phys. Rev. Lett. 107, 107601 (2011)), and low-field magnetic resonance imaging (I. Savukov, et al., J. Magn. Reson. 199, 188 (2009)), require sensitive magnetic measurements in a finite magnetic field. In addition, scalar magnetometers measuring the Zeeman frequency are unique among magnetic sensors in being insensitive to the direction of the field, making them particularly suitable for geomagnetic mapping (M. N. Nabighian, et al., Geophysics 70, 33ND (2005)) and field measurements in space (A. Balogh, Space Sci. Rev. 152, 23 (2010); N. Olsen, et al., Space Sci. Rev. 155, 65 (2010)). Highly sensitive magnetometers, particularly magnetometers that do not require near zero-magnetic fields, are therefore desirable.